Rotary or roller crushing units (also known as “crushers”) can be used for crushing or sizing oil sands immediately taken from haul trucks or other vehicles prior to secondary sizing using crushers, breakers and vibratory screens. Oil sands can contain both soft chunks of ore that are clumped together, as well as heavier and denser chunks. The oil sands can also include solid rock that is capable of shearing a crusher tooth completely off of the crusher.
An example of a known design of a crusher tooth is shown in FIGS. 1A and 1B. A tooth of this design may have a mass of roughly 20 kg, and is approximately 283 mm tall and 160 mm in diameter at its extremities. A typical design includes a forged 4340QT blank in the rough shape of tooth (A) that is then machined to size, and robotically overlaid with tungsten carbide overlays (B), (C) and (D) using plasma-transfer arc welding (“PTAW”). Overlay (B) is approximately 6 mm thick, whereas overlay (C), placed adjacent to overlay (B), and overlay (D), placed around the circumference of tooth (A), are approximately 3 mm thick. In some embodiments, overlay (C) is a 3 mm layer of tungsten carbide applied to tooth (A) first, with a second 3 mm layer of tungsten carbide applied on top of overlay (C) to form overlay (B).
A problem with this prior art design is that the thickness of each tungsten carbide overlay layer is limited by practical adhesion limits. Tungsten carbide cannot be reliably overlaid onto a tooth in thicknesses greater than 6 mm without experiencing overlay degradation and delamination. In other words, the overlay thickness cannot simply be increased to achieve improved wear life. Crusher teeth of this design can have a wear-life of as little as 5 weeks, and even less in winter months or under harsh operating conditions.
It is, therefore, desirable to provide an improved tooth for a roller crusher that overcomes the shortcomings of the prior art.